summaryrefslogtreecommitdiffstats
path: root/arch/x86/lib/clear_page_64.S
blob: 2760a15fbc002581c81bbb74200ef579cc613575 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
/* SPDX-License-Identifier: GPL-2.0-only */
#include <linux/export.h>
#include <linux/linkage.h>
#include <asm/asm.h>

/*
 * Most CPUs support enhanced REP MOVSB/STOSB instructions. It is
 * recommended to use this when possible and we do use them by default.
 * If enhanced REP MOVSB/STOSB is not available, try to use fast string.
 * Otherwise, use original.
 */

/*
 * Zero a page.
 * %rdi	- page
 */
SYM_FUNC_START(clear_page_rep)
	movl $4096/8,%ecx
	xorl %eax,%eax
	rep stosq
	RET
SYM_FUNC_END(clear_page_rep)
EXPORT_SYMBOL_GPL(clear_page_rep)

SYM_FUNC_START(clear_page_orig)
	xorl   %eax,%eax
	movl   $4096/64,%ecx
	.p2align 4
.Lloop:
	decl	%ecx
#define PUT(x) movq %rax,x*8(%rdi)
	movq %rax,(%rdi)
	PUT(1)
	PUT(2)
	PUT(3)
	PUT(4)
	PUT(5)
	PUT(6)
	PUT(7)
	leaq	64(%rdi),%rdi
	jnz	.Lloop
	nop
	RET
SYM_FUNC_END(clear_page_orig)
EXPORT_SYMBOL_GPL(clear_page_orig)

SYM_FUNC_START(clear_page_erms)
	movl $4096,%ecx
	xorl %eax,%eax
	rep stosb
	RET
SYM_FUNC_END(clear_page_erms)
EXPORT_SYMBOL_GPL(clear_page_erms)

/*
 * Default clear user-space.
 * Input:
 * rdi destination
 * rcx count
 * rax is zero
 *
 * Output:
 * rcx: uncleared bytes or 0 if successful.
 */
SYM_FUNC_START(rep_stos_alternative)
	cmpq $64,%rcx
	jae .Lunrolled

	cmp $8,%ecx
	jae .Lword

	testl %ecx,%ecx
	je .Lexit

.Lclear_user_tail:
0:	movb %al,(%rdi)
	inc %rdi
	dec %rcx
	jnz .Lclear_user_tail
.Lexit:
	RET

	_ASM_EXTABLE_UA( 0b, .Lexit)

.Lword:
1:	movq %rax,(%rdi)
	addq $8,%rdi
	sub $8,%ecx
	je .Lexit
	cmp $8,%ecx
	jae .Lword
	jmp .Lclear_user_tail

	.p2align 4
.Lunrolled:
10:	movq %rax,(%rdi)
11:	movq %rax,8(%rdi)
12:	movq %rax,16(%rdi)
13:	movq %rax,24(%rdi)
14:	movq %rax,32(%rdi)
15:	movq %rax,40(%rdi)
16:	movq %rax,48(%rdi)
17:	movq %rax,56(%rdi)
	addq $64,%rdi
	subq $64,%rcx
	cmpq $64,%rcx
	jae .Lunrolled
	cmpl $8,%ecx
	jae .Lword
	testl %ecx,%ecx
	jne .Lclear_user_tail
	RET

	/*
	 * If we take an exception on any of the
	 * word stores, we know that %rcx isn't zero,
	 * so we can just go to the tail clearing to
	 * get the exact count.
	 *
	 * The unrolled case might end up clearing
	 * some bytes twice. Don't care.
	 *
	 * We could use the value in %rdi to avoid
	 * a second fault on the exact count case,
	 * but do we really care? No.
	 *
	 * Finally, we could try to align %rdi at the
	 * top of the unrolling. But unaligned stores
	 * just aren't that common or expensive.
	 */
	_ASM_EXTABLE_UA( 1b, .Lclear_user_tail)
	_ASM_EXTABLE_UA(10b, .Lclear_user_tail)
	_ASM_EXTABLE_UA(11b, .Lclear_user_tail)
	_ASM_EXTABLE_UA(12b, .Lclear_user_tail)
	_ASM_EXTABLE_UA(13b, .Lclear_user_tail)
	_ASM_EXTABLE_UA(14b, .Lclear_user_tail)
	_ASM_EXTABLE_UA(15b, .Lclear_user_tail)
	_ASM_EXTABLE_UA(16b, .Lclear_user_tail)
	_ASM_EXTABLE_UA(17b, .Lclear_user_tail)
SYM_FUNC_END(rep_stos_alternative)
EXPORT_SYMBOL(rep_stos_alternative)